1. Field of the Invention
The present invention relates to a scanner, and more specifically, to a charge coupled device (CCD) scanner powered by a serial bus.
2. Description of the Prior Art
Please refer to FIG. 1 and FIG. 2. FIG. 1 is a schematic view of a charge coupled device (CCD) scanner 10 electrically connected to both a universal serial bus (USB) 30 and an external power source 20 according to the prior art. FIG. 2 is a function block diagram of the scanner 10 in FIG. 1. The scanner 10 includes a scanning module 14 for generating image data by way of scanning a document 12, a motor 22 for driving the scanning module 14, and a control circuit 24 for controlling operations of the scanner 10. The scanning module 14 further includes a light source 16 for illuminating the document 12 and a CCD 18 for detecting light reflected form the document 12 so as to generate the image data of the document 12. The USB 30 further includes a power rail 32 to provide a power of 2.5 Watts (W). The specification of the power rail 32 is defined by companies including IBM, Intel, Microsoft, NEC, Compaq, DEC, Northern Telecom, etc. and is omitted for simplicity of description.
The scanner 10 is electrically connected to a sufficient power source to ensure the operation of the scanner 10. Normally, a cathode ray tube, employed as the light source 16 of the scanner 10, consumes a power of at least 16 W. In addition, the CCD 18 of the scanner 10, the motor 22 and the control circuit 24 consume powers of 0.5 W, 1.5 W and 0.5 W, respectively. Thus the total consumption of power during the operation of the scanner 10 exceeds the power of 2.5 W provided by the power rail 32 of the USB 30. Consequently, the external power source 20, needing extra space, is needed for the operation of the scanner 10 in addition to the power provided by the power rail 32 of the USB 30.